What is the formula for calculating velocity for a midi keyboard?

Question

MIDI

Hello community.
A dead midi keyboard fell into my hands, I collect and program new brains for it.
The keys are dynamic, and you can measure the time interval between half-pressing and actually pressing the key to the "floor".
This interval varies from 5 to 300 milliseconds. Velocity in the protocol - from 0 to 127.
Pressing a medium force on the working key gives a value of about 50-70; to jump to the top, you need to directly wet the "tool".
I ask you to suggest what formula should be used to calculate the output value of the force. Google didn't help)